The young male lynx was last seen in the Guadiana Valley in the Algarve in 2016, just days after his release into the wild as part of a project to save the endangered species. The GPS signal from a device on his collar then disappeared, and for two years, his whereabouts were unknown.
He has now become the first Iberian lynx seen in Catalonia for more than a hundred years, after conservation officials tracked him down to a wooded area in Barcelona following reports of sightings.
To avoid attracting curious crowds, authorities have declined to release details of his location.
Conservation officials released pictures of the lynx lounging under the shade of a tree, apparently in good health and unfazed by his surroundings.
They are now working with experts from IberLince, the EU-funded rehabilitation programme, on a plan to capture Lithium as he is "in an unsuitable location to guarantee his security", close to roads and urban centres.
"This is the first time the presence of an Iberian Lynx has been detected in Catalonia since the beginning of the 20th century," they said in a statement.
Santi Palazón, a biologist from the Catalan Generalitat's Flora and Fauna Service, told El Periodico newspaper that while the "adventurous" lynx seemed to have adapted to his environment, it "made no sense to leave him in Catalonia, alone".
The lynx's trek across the Iberian Peninsula - crossing mountains, valleys and rivers - is all the more impressive given that a previous attempt to introduce him to the wild ended in failure.
He was last seen two years ago in the Guadiana Valley, southeastern Portugal
Born in 2014 in a captive breeding centre in the southern Spanish region of Andalusia, Lithium was first released the following year but was recaptured in early 2016 as he was struggling to adapt.
Showing signs of weakness, he spent a spell at an endangered species recovery centre before his second release.
Iberian Lynx numbers dwindled to just 94 in 2002 but rehabilitation efforts are paying off, with 589 found in a 2017 provisional census of the species.
Comment: What is it with scientists trying to play god? Granted humans have driven many species to extinction and the intent behind many conservation efforts are admirable, but judging by the repeated problems scientists are encountering, clearly they don't know what's best for these endangered species: